|Publication number||US4429469 A|
|Application number||US 06/320,523|
|Publication date||Feb 7, 1984|
|Filing date||Nov 12, 1981|
|Priority date||Nov 13, 1980|
|Publication number||06320523, 320523, US 4429469 A, US 4429469A, US-A-4429469, US4429469 A, US4429469A|
|Inventors||Noboru Tsushima, Makoto Tomoyori, Masatoshi Harumatsu|
|Original Assignee||Alps Electric Co., Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (51), Classifications (11), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to an apparatus for detecting the direction of a moving vehicle in which a geomagnetic azimuth detector and a turning angle detector are combined.
Heretofore, apparatuses utilizing geomagnetism, for example, the so-called magnetic compass, utilizing the rotation of a magnet, have been often employed in order to detect and indicate the traveling direction of a moving vehicle such as automobile. In such apparatuses, however, a considerable reading error develops due to the vibration or turning of the moving vehicle. As apparatuses free from the disadvantage, there have been devised various devices which apply a method of directly converting a geomagnetic azimuth into an electrical signal, in other words, a flux-gate magnetometer, or which utilize a magnetosensitive device such as Hall device and magnetoresistor.
However, insofar as the method of detecting the geomagnetism is relied on, a precise azimuth signal cannot be obtained in a region where a magnetic disturbance occurs, such as an intense-field region.
As other methods for detecting the direction of a moving object, dynamic turning-angle detecting methods have been devised.
Among apparatuses employing the methods, the most precise apparatus is a gyro-compass. The gyro-compass, however, is very expensive and difficult to be used in mass-produced vehicles, such as automobiles. Besides, for the overland traveling, it is also possible to detect the turning angle of steering or the like. With this method, however, an accumulated error, due to the use for a long term, may become great. In the dynamic turning-angle detection, the most serious disadvantage is that the geographic azimuth cannot be detected at all.
The present invention has been made in view of the drawbacks described above, and has for its object to provide a direction detection apparatus which can indicate the traveling direction of a moving vehicle as a geographical azimuth on the basis of geomagnetic detection and which can always indicate a precise traveling direction as a geographical azimuth even in a region involving a magnetic disturbance such as an intense magnetic field.
According to one aspect of performance of the present invention, a direction detection apparatus is characterized by comprising a magnetic sensor which senses a geomagnetic azimuth, a turning-angle sensor which senses a turning angle dynamically, a magnetic-disturbance detector which detects a magnetic disturbance on the basis of the output of said magnetic sensor, and a signal switching device which applies either the magnetic sensor output or the turning-angle sensor output to a display device in accordance with a signal from the magnetic-disturbance detector.
FIG. 1 is a block diagram showing the fundamental construction of a direction detection apparatus according to the present invention,
FIG. 2 is a schematic constructional view of the direction detection apparatus installed on an automobile,
FIGS. 3(a) and 3(b) are schematic views of the head portion of a flux-gate magnetic sensor in the case of employing a toroidal core,
FIG. 4 is a diagram of the fundamental circuit arrangement of the flux-gate magnetic sensor,
FIG. 5 is a graph showing the variation of the output of the flux-gate magnetic sensor depending upon the geomagnetic azimuth,
FIGS. 6(a) and 6(b) are vector diagrams each showing the change of a geomagnetic vector due to a typical magnetic disturbance.
FIG. 7 is a flow chart showing an embodiment of the principle of detecting a magnetic disturbance, and
FIG. 8 is a more detailed block diagram of an embodiment of the direction detection apparatus according to the present invention.
Hereunder, the present invention will be described in conjunction with embodiments.
FIG. 1 is a diagram showing the fundamental construction of the present invention. In the figure, numeral 1 designates a magnetic sensor which generates an electric signal corresponding to a geomagnetic azimuth. On the basis of an output signal from the magnetic sensor 1, a magnetic-disturbance detector 2 detects a magnetic disturbance and generates a magnetic disturbance detection signal. Using the output signal from the magnetic sensor 1, an azimuth calculating device 3 calculates the geomagnetic azimuth and generates an azimuth signal. A turning-angle sensor 4 senses the turning angle of a moving object or the like dynamically and generates a signal corresponding to the turning angle. Numeral 6 designates an azimuth display device which executes the correction processing of a magnetic deviation on the basis of either the azimuth signal from the azimuth calculating device 3 or the turning-angle signal from the turning-angle sensor 4, and which can display a geographic azimuth. In the presence of the magnetic disturbance, a signal switching device 5 responds to the magnetic-disturbance detection signal generated by the magnetic-disturbance detector 2 and supplies the azimuth display device 6 with the turning-angle signal of the turning-angle sensor 4 instead of the azimuth signal generated by the azimuth calculating device 3. More specifically, in a region free from any magnetic disturbance, the geographic azimuth with the magnetic deviation corrected is displayed on the azimuth display device 6 on the basis of the azimuth signal obtained from the magnetic sensor 1 and the azimuth calculating device 3. On the other hand, in case where the moving object has advanced into a region involving the magnetic disturbance, the magnetic-disturbance detection signal is transmitted to the signal switching device 5 by the magnetic-disturbance detector 2. Due to the operation of the signal switching device 5, in the display device 6, the azimuth immediately before the magnetic disturbance is stored, and the azimuth of the moving object is evaluated from the stored azimuth and the turning-angle signal transmitted from the turning-angle sensor 4 and then displayed.
In this way, the traveling direction of the moving object in the magnetic-disturbance region can be displayed on the azimuth display device 6 in terms of the geographic azimuth. When the moving object has advanced into the region free from the magnetic disturbance again, the magnetic-disturbance detector 2 fails to generate the disturbance detection signal. As a result, the signal switching device 5 transmits the azimuth signal of the device 3 to the display device 6 again, and the azimuth display device 6 displays the azimuth based on the azimuth signal of the device 3.
FIG. 2 is a schematic constructional view in the case where the apparatus according to the present invention is installed on an automobile by way of example. In the figure, numeral 8 designates the automobile body, and numeral 7 an arithmetic circuit which executes the processings of the azimuth calculation, the magnetic-disturbance detection, the signal switching, etc. Parts 1, 4 and 6 are the same as those in FIG. 1.
Now, there will be described an embodiment of the magnetic sensor which can process a geomagnetic azimuth as an electrical signal.
FIGS. 3(a) and 3(b) are schematic views of the head portion of a flux-gate magnetic sensor employing a toroidal core.
In FIG. 3(a), numeral 9 designates a saturable core of high permeability, and numeral 10 an exciting coil for applying an alternating field to the saturable core 9. In FIG. 3(b), numeral 9' indicates a core portion with the exciting coil omitted from the illustration of FIG. 3(a), and numerals 11 and 12 indicate detecting coils which detect the x-directional component and y-directional component of an external input magnetic field H, respectively. When an alternating current is caused to flow through the exciting coil 10 at a frequency f so as to establish an alternating field at which the core 9 becomes above its saturation flux density, secondary high-frequency voltages at excitation frequencies proportional to the x- and y-directional components of the input field H, i.e., Hx =H cos θ and Hy =H sin θ are respectively generated in the detecting coils 11 and 12. That is, the voltage Vx2f =K' Hx is generated in the detecting coil 11, and the voltage Vy2f =K' Hy in the detecting coil 12. Here, K' denotes a constant which is determined by the exciting condition.
FIG. 4 is a block diagram of the fundamental circuit arrangement of the flux-gate magnetic sensor. In the figure, numeral 13 designates the sensor head portion shown in FIG. 3, numeral 14 an oscillator circuit which supplies an alternating current to the exciting coil of the head portion 13, numeral 15 a current amplifier circuit which amplifies an output from the oscillator circuit 14, numeral 16 a band-pass filter which passes only the secondary high frequency of an output from the head portion 13, numeral 17 an amplifier circuit, numeral 18 a synchronous rectifier circuit which phase-discriminates an output from the amplifier 17 and inverts the discriminated output into a direct current, and numeral 19 a frequency multiplier circuit which gives the synchronous rectifier circuit 18 a reference phase. The circuits 16, 17 and 18 are disposed in the numbers of two in correspondence with the x-directional component and y-directional component. Owing to such circuit arrangement, the following output voltages Vx and Vy are respectively obtained in correspondence with the x- and y-directional components of the input field H:
Vx =K Hx =K H cos θ
Vy =K Hy =K H sin θ
Here, K denotes a constant which is determined by circuit conditions.
FIG. 5 illustrates the variations of the magnetic sensor outputs Vx and Vy indicated in FIG. 4 in the case where the input magnetic field is the geomagnetism. In the figure, a curve l1 corresponds to the output Vx, and a curve l2 to the output Vy. When the magnetic sensor is facing the magnetic north N, the voltage Vx becomes the maximum in the plus direction. Conversely, when it is facing the magnetic south S, the voltage Vx becomes the maximum in the minus direction. Similarly, the voltage Vy assumes the maximum plus value at the magnetic east E and the maximum minus value at the magnetic west W. Therefore, the geomagnetic azimuth θ in the case where the magnetic sensor is fixed can be obtained by executing the following operation:
θ=tan-1 (Vy /Vx)
When the voltages Vx and Vy are calculated every fixed time by the use of reference clock pulses, the geomagnetic azimuth θ changing each time can be digitally calculated. In other words, an azimuth θn at a time tn can be expressed as follows:
θn =tan-1 (Vy.sbsb.n /Vx.sbsb.n)
In addition, the detection of a magnetic disturbance is permitted by employing a magnetic sensor which can provide the output voltages Vx and Vy corresponding to the x- and y-directional components of the geomagnetism every fixed time as described above.
Now, the principle of the magnetic disturbance detection will be stated.
FIGS. 6(a) and 6(b) show the disturbances of the geomagnetism due to magnetic disturbances as vector diagrams. In the figures, numeral 20 indicates a geomagnetism vector H, symbols 21a and 21b indicate disturbing magnetism vectors Hd respectively, and symbols 22a and 22b indicate the resultant vectors Hex between the geomagnetism vectors and the disturbing magnetism vectors respectively. Actually detected by the magnetic sensor due to the magnetic disturbance is not the geomagnetism 20, but is the resultant vector between the geomagnetism vector 20 and the disturbing magnetism vector 22a or 22b.
Therefore, the presence or absence of the magnetic disturbance can be detected by comparing the magnitude of the original geomagnetism vector H and that of the resultant vector Hex between the geomagnetism vector B and the disturbance vector Hd. Depending upon the disturbing magnetism vector Hd, |Hex |=|H| can hold. Since, however, the disturbing magnetism vector is not constant, it is allowed to judge that |Hex |=|H| hardly holds.
Therefore, the detection of the magnetic disturbance can be satisfactorily executed by the comparison between |Hex | and |H|. That is, the occurrence of the magnetic disturbance can be detected by detecting the magnitude of the magnetism vector every fixed time by the use of the reference clock and always comparing it with the immediately preceding value. More specifically, when the flux-gate magnetic sensor illustrated in or by FIGS. 3(a) and 3(b), FIG. 4 and FIG. 5 is used, the output voltages corresponding to the x- and y-directional components Hx and Hy of the magnetism vector H become Vx =K Hx and Vy =K Hy respectively.
In the absence of the magnetic disturbance, the resultant vector Hex in FIG. 6(a) or 6(b) is equivalent to the geomagnetism vector H, and hence, the output voltages of the magnetic sensor become:
Vx =K|Hex | cos θ
Vy =K|Hex | sin θ
Since Vx 2 +Vy 2 =K2 |Hex |2 is obrained from them, |Hex |2 =(Vx 2 +Vy 2)/K2 holds, and the value of (Vx 2 +Vy 2) can be used instead of the value of |Hex |. That is, the output voltages corresponding to a geomagnetism vector Hn =Hex.sbsb.n at a time tn are:
Vx.sbsb.n =K|Hex.sbsb.n | cos θ and Vy.sbsb.n =K|Hex.sbsb.n | sin θ.
Supposing that a magnetic disturbance has occurred at a time tn+1, the relationship between a resultant magnetism vector Hex.sbsb.n+1 and a geomagnetism vector Hn+1 at the time tn+1 becomes |Hex.sbsb.n+1 |≠|Hn+1 |=|Hn |. When expressed with the output voltages of the magnetic sensor, this becomes:
(Vx.sbsb.n+12 +Vy.sbsb.n+12)≠(Vx.sbsb.n2 +Vy.sbsb.n2)
By putting Vx.sbsb.n2 +Vy.sbsb.n2 =Vn 2 and Vx.sbsb.n+12 +Vy.sbsb.n+12 =Vn+1 2 and comparing Vn 2 and Vn+1 2, it can be judged for Vn 2 ≠Vn+1 2 that the magnetic disturbance has occurred at the time tn+1. In actuality, the output voltage involves slight steady fluctuations. Therefore, a minute fluctuation in V2 ascribable to the steady minute voltage fluctuations is set at ΔVo as its initial value, and the output voltages at the time tn and at the time tn+1 when the magnetic disturbance has occurred are compared. By putting Vn 2 -Vn+1 2 =ΔV, the presence of the magnetic disturbance is represented by ΔVo <|ΔV|. In contrast, in the absence of the magnetic disturbance, ΔVo ≧|ΔV| holds. Therefore, the presence or absence of the magnetic disturbance can be detected by performing such comparing operations.
FIG. 7 shows a flow chart of the foregoing principle of the magnetic disturbance detection. In the figure, numeral 23 indicates Vx.sbsb.n and Vy.sbsb.n at the time tn as are applied by the magnetic sensor. A step 24 is for the calculating processing of Vx.sbsb.n2 +Vy.sbsb.n2 =Vn 2, and a step 25 is for the calculating processing of the difference from a value at the immediately preceding time tn-1, i.e., Vn-1 2 -Vn 2 =ΔV. A step 26 is for the decision by the comparison between the initial set value ΔVo and |ΔV|. In this step, it is decided for ΔVo ≧|ΔV| that no magnetic disturbance exists at the time tn. In a step 27, Vn 2 is stored. Further, using inputs at a time tn+1, the comparison processings between Vn+1 and Vn are successively performed. On the other hand, when ΔVo <| ΔV| holds, it is decided that a magnetic disturbance has occurred at the time tn. The value Vn-1 2 at the time tn-1 immediately before the magnetic disturbance is stored in a step 28, and a magnetic disturbance signal is delivered in a step 29. The value Vn-1 2 immediately before the disturbance as stored in the step 28 is compared with the value Vn+1 2 of the next time tn+1, and serves as the reference value of the comparisons as long as the magnetic disturbance continues. Supposing that the magnetic disturbance has disappeared at a time tn+m, Vn-1 2 -Vn+m 2 =ΔV is calculated in the step 25, and ΔVo ≧|ΔV| holds in the decision processing 26. Therefore, the magnetic disturbance signal fails to appear, and Vn+m 2 is stored anew in the step 27. Further, the operating processings from the step 23 are successively repeated.
The detection of the magnetic disturbance can be made by a magnetic-disturbance detector which processes the output of the magnetic sensor in this manner.
FIG. 8 is a block diagram of an embodiment of the direction detection apparatus which has the magnetic-disturbance detector as stated above. In the figure, numeral 30 designates a magnetic sensor, and numeral 31 a geomagnetic azimuth-calculating device which evaluates a geomagnetic azimuth from the output of the magnetic sensor 30. A calculating device 32 executes the calculation of Vn 2 in the step 24 in FIG. 7. A magnetic-disturbance detector 33 executes the processings of the steps 25, 26, 27, 28 and 29 in FIG. 7, i.e., the calculation of ΔV and compares it with the initial set value ΔVo, thereby to generate the magnetic disturbance signal in the presence of the magnetic disturbance. Numeral 34 indicates a reference clock generator which generates a reference clock, numeral 35 a turning-angle sensor, and numeral 36 a turning angle-calculating device which calculates a turning angle on the basis of an electrical signal from the turning-angle sensor 35. A signal switching device 37 can switch a signal from the magnetic sensor and a signal from the turning-angle sensor therebetween on the basis of the magnetic disturbance signal from the magnetic-disturbance detector 33. An azimuth display device 38 corrects a magnetic deviation and displays the traveling direction of a moving object as a geographic azimuth.
The azimuth display device 38 includes a correction circuit 39 for correcting the magnetic deviation, a memory circuit 40 for storing an immediately preceding azimuth at the magnetic disturbance, a calculating circuit 41 for evaluating an azimuth from the output of the memory circuit 40 and the turning-angle signal at the magnetic disturbance, and a display 42.
In the absence of the magnetic disturbance, the azimuth signal provided from the correction circuit 39 is indicated on the display 42, whereas in the presence of the magnetic disturbance, the azimuth signal provided from the calculating circuit 41 is indicated thereon.
As set forth above, according to the present invention, a direction detection apparatus is constructed of a magnetic sensor which senses a geomagnetic azimuth, a turning-angle sensor which senses a turning angle dynamically, a magnetic-disturbance detector which detects a magnetic disturbance on the basis of an output of the magnetic sensor, and a signal switching device which applies either the magnetic sensor output or the turning-angle sensor to an azimuth display device or the like on the basis of a signal from the magnetic-disturbance detector. Therefore, not only when a moving object lies in a place free from any magnetic disturbance, but also when it lies in a place undergoing a magnetic disturbance such as intense magnetic field, the traveling direction of the moving object can be detected as a precise geographic azimuth at all times. In addition, the present invention has the advantage that the occurrence of an accumulated error is prevented by, for example, correcting the output of the turning-angle sensor with reference to the geomagnetism. By combining the direction detection apparatus according to the present invention with a speed sensor, the moving object can have its present position detected precisely whatever place it is moving in. The invention is greatly effective in this manner.
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4505054 *||May 25, 1983||Mar 19, 1985||Prince Corporation||Magnetic sensor mounting system|
|US4539760 *||Oct 12, 1983||Sep 10, 1985||Plessey Overseas Ltd.||Compass|
|US4546550 *||Oct 12, 1983||Oct 15, 1985||Plessey Overseas Ltd.||Compass|
|US4546551 *||Mar 24, 1983||Oct 15, 1985||Prince Corporation||Electrical control system|
|US4555761 *||Feb 9, 1983||Nov 26, 1985||Nippon Soken, Inc.||Direction detection for a vehicle|
|US4593359 *||Jun 24, 1983||Jun 3, 1986||Ilan Sadeh||Vehicle navigation system|
|US4633709 *||Aug 7, 1985||Jan 6, 1987||Nippondenso Co., Ltd.||Vehicle turn angle detecting device|
|US4663719 *||Apr 26, 1983||May 5, 1987||Nippon Soken, Inc.||Method and apparatus for display of distance and direction to destination|
|US4677381 *||Oct 19, 1984||Jun 30, 1987||Prince Corporation||Flux-gate sensor electrical drive method and circuit|
|US4680866 *||Dec 19, 1985||Jul 21, 1987||Honeywell Inc.||Magnetic flux detector correction system|
|US4791574 *||Aug 25, 1986||Dec 13, 1988||U.S. Philips Corporation||Land vehicle navigation device comprising a filter unit for determining an optimum heading from presented orientation signals, and filter unit to be used in said navigation device|
|US4831563 *||Jul 1, 1987||May 16, 1989||Pioneer Electronic Corporation||Method of processing output data from geomagnetic sensor|
|US4862398 *||Nov 13, 1987||Aug 29, 1989||Sumitomo Electric Industries, Ltd.||Correcting method and correcting errors in a terrestrial magnetism heading sensor|
|US4866384 *||May 11, 1987||Sep 12, 1989||Gec-Marconi Limited||Relative phase magnetic field direction indicating devices useful as compasses|
|US4890233 *||Oct 27, 1987||Dec 26, 1989||Pioneer Electronic Corporation||Vehicle bearing detection and data processing methods applicable to vehicle navigation system|
|US5021962 *||Oct 22, 1987||Jun 4, 1991||Robert Bosch Gmbh||Navigation method for vehicles with electronic compass|
|US5122960 *||Oct 10, 1989||Jun 16, 1992||Sumitomo Electric Industries, Ltd.||Locator for a moving body|
|US5151862 *||May 20, 1991||Sep 29, 1992||Nissan Motor Company, Ltd.||Vehicular traveling direction measuring system|
|US5161311 *||May 13, 1992||Nov 10, 1992||Alps Electric Inc.||Calibration and compensation of an electronic compass system|
|US5235514 *||Mar 25, 1991||Aug 10, 1993||Sumitomo Electric Industries, Ltd.||Apparatus for estimating current heading using magnetic and angular velocity sensors|
|US5297050 *||Nov 6, 1991||Mar 22, 1994||Fujitsu Ten Limited||Direction sensor having an earth magnetism sensor and a rate gyro sensor and navigation system having this direction sensor|
|US5394029 *||Feb 17, 1993||Feb 28, 1995||Gay; John C.||Geomagnetic orientation sensor, means, and system|
|US5444916 *||Oct 28, 1993||Aug 29, 1995||Sato Kogyo Co., Ltd.||Electronic stereo clino-compass|
|US5481808 *||Apr 10, 1995||Jan 9, 1996||U.S. Philips Corporation||Vehicle orientation sensor and method with magnetic stabilization|
|US5664335 *||Jun 6, 1995||Sep 9, 1997||Prince Corporation||Vehicle compass circuit|
|US5737226 *||Jun 5, 1995||Apr 7, 1998||Prince Corporation||Vehicle compass system with automatic calibration|
|US5878370 *||Dec 1, 1995||Mar 2, 1999||Prince Corporation||Vehicle compass system with variable resolution|
|US5953683 *||Oct 9, 1997||Sep 14, 1999||Ascension Technology Corporation||Sourceless orientation sensor|
|US6301794||May 27, 1999||Oct 16, 2001||Johnson Controls, Inc.||Vehicle compass system with continuous automatic calibration|
|US6523271 *||Jul 20, 2001||Feb 25, 2003||Seiko Instruments Inc.||Method of adjusting drive current of magnetism sensor and electronic azimuth meter|
|US6539639 *||Dec 6, 2000||Apr 1, 2003||Honeywell International Inc.||Monitoring accuracy of an electronic compass|
|US6643941||Jul 24, 2001||Nov 11, 2003||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US6857194 *||Sep 16, 2003||Feb 22, 2005||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US6964108||Dec 1, 2004||Nov 15, 2005||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US7127823||Nov 10, 2005||Oct 31, 2006||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US7191533||Aug 29, 2006||Mar 20, 2007||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US7353614 *||Feb 22, 2007||Apr 8, 2008||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US7458166||Jan 29, 2008||Dec 2, 2008||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US7543392 *||Nov 8, 2004||Jun 9, 2009||Samsung Electronics Co., Ltd.||Motion estimation method and system for mobile body|
|US20040123475 *||Sep 16, 2003||Jul 1, 2004||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US20050091861 *||Dec 1, 2004||May 5, 2005||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US20050125108 *||Nov 8, 2004||Jun 9, 2005||Samsung Electronics Co., Ltd.||Motion estimation method and system for mobile body|
|US20060075646 *||Nov 10, 2005||Apr 13, 2006||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US20060288597 *||Aug 29, 2006||Dec 28, 2006||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US20070163132 *||Feb 22, 2007||Jul 19, 2007||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|US20080120054 *||Jan 29, 2008||May 22, 2008||Johnson Controls Technology Company||Vehicle compass system with continuous automatic calibration|
|USRE33025 *||Nov 5, 1987||Aug 15, 1989||Nippon Soken, Inc.||Method and apparatus for display of distance and direction to destination|
|DE4128740A1 *||Aug 29, 1991||Mar 5, 1992||Alps Electric Usa||Electronic compass with direction signal compensation - employs common software in manual and automatic modes using maxima and minima of orthogonal pick=up voltages|
|EP0179634A2 *||Oct 18, 1985||Apr 30, 1986||Prince Corporation||Flux-gate sensor electrical drive method and circuit|
|EP0268278A2 *||Nov 17, 1987||May 25, 1988||Sumitomo Electric Industries Limited||A correcting method for correcting errors in a terrestrial magnetism heading sensor|
|EP0373317A2 *||Oct 11, 1989||Jun 20, 1990||Sumitomo Electric Industries, Ltd.||Device and method for determining errors in the data of a magnetic direction sensor|
|U.S. Classification||33/361, 33/356, 702/150|
|International Classification||G01P13/04, G01C17/38, B62D15/00, G01C17/30, G01C21/00, G01R33/04|
|Jul 16, 1987||FPAY||Fee payment|
Year of fee payment: 4
|Jul 22, 1991||FPAY||Fee payment|
Year of fee payment: 8
|Jul 11, 1995||FPAY||Fee payment|
Year of fee payment: 12